The art has seen cartridge assemblies in which brachytherapy seeds are loaded prior to shipping and dispensement of the seeds into an elongate cannula, or seed applicator, from which they are then implanted into a patient. Brachytherapy seed cartridges are provided with a number of radioactive brachytherapy seeds, e.g. I-125 or Pd-103 seeds, and used as a supply source of those seeds to be loaded into a seed applicator. FIGS. 1 and 2A-C depict a typical seed cartridge 10 manufactured and sold by Mick Radio-Nuclear Instruments, Inc. of Mount Vernon, N.Y., U.S.A. Cartridge 10 includes a magazine 12 and a cap 14. Magazine 12 includes an elongate seed channel 16 for receiving transversely-aligned brachytherapy seeds 18 and dispense aperture 20 from which the seeds are dispensed into the applicator. Cap 14 supports an elongate plunger 22 which is spring-biased to extend into channel 16 and urge the seeds 18 towards dispense aperture 20. Magazine 12 further includes an external helical thread 24 for mating with an internal helical thread, not shown, within cap 14. Cap 14 includes an external thread 26 to secure the assembled cartridge 10 in a V-block for steam sterilization.
To form a disposable, or single-use, cartridge 10, magazine 12 and cap 14 are typically made of a suitable plastic material capable of withstanding steam sterilization. Alternatively, cap 14 may be formed from stainless steel or brass in order to provide some degree of shielding. This later feature recognizes that a technician holding a cartridge component in each hand while threading the two components together risks radiation exposure which should be minimized further. While a technician can work behind an 1-block type shield, that will only help with body exposure. Hand (extremity) exposure remains high due to the dexterity needed to mate and screw the two parts together, due to the proximity of the radioactive seeds to the technician's hands and fingers.
As the cartridge assembly contains radioactive seeds it is extremely important to consider radiation shielding. Shielding is considered important from a manufacturing perspective; ALARA (As Low As Reasonably Achievable) is a commonly used acronym to ensure employee radiation exposure is reduced by means of procedure, controls and personal protective equipment. Shielding is also an extremely important aspect of marketing a radioactive source, such as a seed. Manufacturers that consider occupational exposure to their products, and the reduction thereof, are being proactive in distributing the safest product possible. Shielding of this product would offer lower occupational exposure levels to physicians and their staff in the clinical use of the product. The cartridge assemblies currently used expose the user or handler to radiation immediately adjacent the seeds as well as along the line of sight to any visible (unshielded) seeds.
In addition to shielding it is very important to consider the time of exposure to a radiation source. This aspect relates both to the manufacturing assembly of the loaded cartridge as well as to the event where an end user disassembles and then re-assembles a cartridge. The currently-used cartridge assemblies are threaded together at the top and bottom. To join or disassemble the two parts requires time and also a bit of dexterity as the mating threads may require up to seven full revolutions of the component parts. During the whole process the technician will be exposed to the radiation of the seeds. Moreover, in the event of mal-assembly such as cross threading, the plastic magazine 12, with the seeds loaded into it, may become damaged and cause both a longer period of exposure to the technician and a loss of the cartridge assembly.
The existing cartridge assemblies are described and marketed as being shielded and disposable, but only provide shielding in a portion of the cartridge areas. There is therefore a need for a brachytherapy seed cartridge assembly that will greatly reduce, or even eliminate, radiation exposure to the users and handlers of the cartridge during loading, transportation, and use.